The present invention relates to a fabrication technique for a semiconductor integrated circuit device and more particularly to a technique which is effective in its application to an exposure technique used in a fabrication process for a semiconductor integrated circuit device.
A photomask which the present inventors have studied is a resist mask using a photosensitive organic film (photoresist film) as a shield against exposure light. This photomask can be expected to afford a cost reducing effect because it does not include an etching step for a metallic film such as a chromium film. Besides, there accrues an advantage in point of ensuring a high accuracy of pattern size. Further, the photomask manufacturing TAT can be greatly shortened.
As to the technique of using a photosensitive organic film as a light shield, it is disclosed, for example, in Japanese Published Unexamined Patent Application No. Hei 5(1993)-289307.
Moreover, in Japanese Published Unexamined Patent Application No. Hei 11(1999)-15133 there is disclosed an example of a pattern forming method in which a pattern included in a group of patterns arranged periodically and located at the outermost peripheral position is mask-biased.
In Japanese Published Unexamined Patent Application No. Hei 6(1994)-19115 is disclosed a technique in which there is applied such a mask-bias as minimizes a dimensional variation of resist caused by a focal shift during exposure.
Further, in Japanese Patent Application No. 2000-246506 is disclosed a resist mask reproducing technique.
However, the present inventors have found out that the above-mentioned exposure techniques using the above resist mask involves the following problems.
If the size of the shield member which is a metallic film such as a chromium film used in an ordinary photomask and that of the shield member used in the above resist mask are set equal to each other, there arises a difference in size between a pattern transferred using the ordinary mask and a pattern transferred using the resist mask.
In the resist mask, the light shielding performance of the photoresist film which constitutes the shield member is inferior to that of such a metallic film as a chromium film and therefore it is necessary that the thickness of the photoresist film be made larger than that of the metallic film. Consequently, a vertical structure of the resist mask becomes larger and there is a fear that the light intensity in an aperture may be decreased under the influence of a waveguide effect. Thus, a decrease in light intensity caused by the waveguide effect is unavoidable. For example, in the case of KrF excimer laser beam with an exposure wavelength xcex=248 nm and in case of optical constants n=2 and k=0.3 of the resist mask being developed by the present inventors, a photoresist film thickness of about 0.45 xcexcm is needed for obtaining a light shielding performance of 3 in terms of OD value. Using these numerical values, we have checked by calculation the influence of the vertical structure of the resist mask and found that the light intensity transmitted by an aperture decreased. It turned out for the first time by the present inventors that the amount of a dimensional variation caused by such a decrease in light intensity was about 40 nm on the upper surface of a semiconductor wafer. Therefore, if the resist mask is fabricated while setting the shield size equal to that of the ordinary photomask, the light intensity distribution on wafer will become different between the ordinary photomask and the resist mask. In many cases, the mask size is optimized using the ordinary photomask, so the mask size of the resist mask does not correspond to an optimal size. This problem arises in case of changing from the exposure treatment using the resist mask to the same treatment using the ordinary photomask or vice versa.
It is an object of the present invention to provide a technique which can improve the pattern accuracy of a semiconductor integrated circuit device.
The above and other objects and novel features of the present invention will become apparent from the following description and the accompanying drawings.
The following is a brief description of a typical invention disclosed herein.
In replacing a photomask with a shield member formed by a metallic film and a photomask with a shield member formed by a photosensitive organic film from one to the other, the present invention involves the steps of applying a dimensional correction responsive to exposure conditions to the shield member formed by the metallic film or the shield member formed by the photosensitive organic film and performing a reducing projection exposure of predetermined patterns to a wafer using the photomask after the dimensional correction.